This invention relates generally to compact, high-efficiency, electrically small loop antennas for use in both transmitters and receivers of portable communication devices. The physical size of modem compact communication devices (such as radio tags, personal communicators and pagers) is often dictated by the size of the antenna needed to make them function effectively. To avoid devices that are too large, pagers have made use of electrically small rectangular loop antennas as receiving only antennas with the maximum dimension of any antenna elements that constitute the antenna on the order of one-tenth or less of the signal wavelength at the receiving frequency. However, these small antennas tend to be inefficient as a result of their very low radiation resistance and comparatively high loss resistance. Likewise, as a result of their high reactive impedance they tend to be sensitive to their physical environment. These small antennas can cause parasitic oscillations in attached radio frequency (RF) circuitry. Finally, because of their low efficiency, these small antennas are inadequate as transmitting antennas.
To overcome the disadvantages of prior art electrically small loop antennas, there is an outstanding need for antennas small in physical dimension (i.e., each element less than one-tenth of the operating wavelength); having relatively high efficiency; capable of being placed in close proximity to associated electronic circuits without adversely affecting performance; capable of being used effectively for both transmitting and receiving; relatively insensitive to orientation and surroundings; easy to manufacture using standard, low-cost components; and capable of having their radiation pattern altered to support different applications. The antenna described below satisfies all these requirements and is unique in design.